Ch. 32 pg. 654-661 Animal cells lack cell walls; supported by proteins like collagen Reproduction and development: Small sperm fertilizes a large non-motile egg, forming a diploid zygote Cleavage – succession of mitotic cell divisions without cell growth between division cycles Blastulta – cleavage leads to the formation of a multicellular stage; takes form of hollow ball Gastrulation – layers of embryonic tissue that will develop into adult body parts are produced; follows blastula stage Gastrula – resulting developmental stage Larva – a sexually immature form of an animal that is morphologically distinct from the adult stage, usually eats different food, and may have a habitat different from the adult. Ex. Tadpole larva of terrestrial frog Metamorphosis – resurgence of development that transforms the animal into an adult Homeoboxes – modules of DNA sequences Ediacaran fauna – named for Edicara Hills of Austrialia where they were first discovered; earliest fossils of animals known; 575 million years old Cambrian explosion – early Cambrian period of Paleozoic Era; first animals with hard mineralized skeletons; more oxygen available, opportunity arose for success of animals

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